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Fatigue is the general term used to describe physical and/or mental weariness which extends beyond normal tiredness.
Physical fatigue concerns the inability to exert force with ones muscles to the degree that would be expected. It may be an overall tiredness of the whole body, or be confined to particular muscle groups. Physical fatigue most commonly results from physical exercise or loss of sleep. Physical fatigue often leads to mental fatigue.
Mental fatigue, which may include sleepiness, concerns a general decrease of attention and ability to perform complex, or even quite simple tasks with customary efficiency. Mental fatigue often results from loss or interruption of the normal sleep pattern and is therefore of great concern to pilots and ATCOs, who are frequently required to work early in the morning or at night.
Sleep patterns are naturally associated with the body's circadian rhythms. Shift patterns and transit across time zones can interrupt circadian rhythms so that, for example, it may be difficult for flight crew or pilots on duty in the early hours of the morning or flight crew operating long-haul routes through multiple time zones to achieve satisfactory rest prior to commencing duty.
It is important to note that people are not the best evaluators of their own alertness state. They are often sleepier than they report.
There are three types of fatigue: transient, cumulative, and circadian:
- Transient fatigue is acute fatigue brought on by extreme sleep restriction or extended hours awake within 1 or 2 days.
- Cumulative fatigue is fatigue brought on by repeated mild sleep restriction or extended hours awake across a series of days.
- Circadian fatigue refers to the reduced performance during nighttime hours, particularly during an individual’s “window of circadian low” (WOCL) (typically between 2:00 a.m. and 05:59 a.m.).
Researches show that the accumulation of "sleep debt", e.g. by having an hour less of sleep for several consecutive days needs a series of days with more-than-usual sleep for a person to fully recover from cumulative fatigue.
Fatigue usually results in impaired standards of operation with increased likeliness of error. For example:
- Increased reaction time;
- Reduced attentiveness;
- Impaired memory; and,
- Withdrawn mood.
In a pilot, fatigue may manifest itself by:
- Inaccurate flying;
- Missed radio calls;
- Symptoms of equipment malfunctions being missed;
- Routine tasks being performed inaccurately or even forgotten; and, in extreme cases,
- Falling asleep - either a short "micro-sleep" or for a longer period.
In an ATCO, fatigue may result in:
- Poor decision making;
- Slow reaction to changing situation;
- Failure to notice an impending confliction;
- Loss of situational awareness;
- Circadian adaptation, i.e. adjustment of the body internal clock (e.g. due to the shift pattern, jet lag, etc.)
- Length of previous rest period;
- Time on duty;
- Time awake prior to duty (duties that start in the evening are more likely to cause fatigue than those beginning at e.g. 8 a.m.)
- Sleep/nap opportunities (during the duty but also at layover destinations)
- Physical conditions (temperature, airlessness, noise, comfort, etc.);
- Workload (high or low);
- Emotional stress (in family life or at work);
- Lifestyle (including sleeping, eating, drinking and smoking habits) and fitness; and,
- Ensure that work schedules, including consecutive shift-working patterns, are constructed so as to have the least possible impact on off duty - and, if applicable, on duty rest.
- Seek to provide optimum working conditions;
- Use Crew Resource Management (CRM) or Team Resource Management (TRM) training to promote awareness to fatigue and sleep issues.
- Establish a Fatigue Risk Management System (FRMS), either as a part of the Safety Management System (SMS) or as a standalone system. An effective FRMS is data-driven and routinely collects and analyzes information and reports related to crew alertness as well as operational flight performance data. Computer models can be used to predict average performance capability from sleep/wake history and normal circadian rhythms.
Pilots and ATCOs
Adopt personal strategies which are likely to decrease the effects of fatigue such as the following:
- Planning activities, meals, rest and sleep patterns during off-duty periods;
- Making the most of permitted rest breaks, including naps;
- Advising colleagues if one detects feeling drowsy;
- Alerting colleagues if they appear to be becoming drowsy.
- Pilot Workload
- Controller Workload
- Fatigue Management: Guidance for Air Traffic Controllers and Air Traffic Engineers
- Flight Crew In-Seat Rest
Accidents & Incidents
Events in the SKYbrary database which include fatigue as a contributory factor:
- A319, vicinity Glasgow UK, 2018 (On 30 September 2018, an Airbus A319 Captain had to complete a flight into Glasgow on his own when the First Officer left the flight deck after suffering a flying-related anxiety attack. After declaring a ‘PAN’ to ATC advising that the aircraft was being operated by only one pilot, the flight was completed without further event. The Investigation found that the First Officer had been “frightened” after the same Captain had been obliged to take control during his attempted landing the previous day and had “felt increasingly nervous” during his first ‘Pilot Flying’ task since the event the previous day.)
- DH8D, Kathmandu Nepal, 2018 (On 12 March 2018, a Bombardier DHC8-400 departed the side of landing runway 20 at Kathmandu after erratic visual manoeuvring which followed a mis-flown non-precision approach to the opposite runway direction and was destroyed. The Investigation concluded that the accident was a consequence of disorientation and loss of situational awareness on the part of the Captain and attributed his poor performance to his unfitness to fly due to mental instability. A history of depression which had led to his release from service as a military pilot and a subsequent period of absence from any employment as a pilot was noted.)
- A320 / B789 / A343, San Francisco CA USA, 2017 (On 7 July 2017 the crew of an Airbus A320, cleared for an approach and landing on runway 28R at San Francisco in night VMC, lined up for the visual approach for which it had been cleared on the occupied parallel taxiway instead of the runway extended centreline and only commenced a go-around at the very last minute, having descended to about 60 feet agl whilst flying over two of the four aircraft on the taxiway. The Investigation determined that the sole direct cause of the event was the poor performance of the A320 flight crew.)
- B773, Hong Kong China, 2017 (On 28 April 2017, a Boeing 777-300 made a 3.2g manual landing at Hong Kong, which was not assessed as such by the crew and only discovered during routine flight data analysis, during a Final Line Check flight for a trainee Captain. The Investigation noted that the landing technique used was one of the reasons the Check was failed. The trainee had been an experienced 737 Captain with the operator who had returned from 777 type conversion training with another airline and was required to undertake line training to validate his command status in accordance with local requirements.)
- AT76, Lisbon Portugal, 2016 (On 22 October 2016, an ATR 72-600 Captain failed to complete a normal night landing in relatively benign weather conditions and after the aircraft had floated beyond the touchdown zone, it bounced three times before finally settling on the runway in a substantially damaged condition. The Investigation noted that touchdown followed an unstabilised approach and that there had been little intervention by the First Officer. However, it tentatively attributed the Captain’s poor performance to a combination of fatigue at the end of a repetitive six-sector day and failure of the operator to provide adequate bounced landing recognition and recovery training.)
- AT72, Karup Denmark, 2016 (On 25 January 2016, an ATR 72-200 crew departing from and very familiar with Karup aligned their aircraft with the runway edge lights instead of the lit runway centreline and began take-off, only realising their error when they collided with part of the arrester wire installation at the side of the runway after which the take-off was rejected. The Investigation attributed the error primarily to the failure of the pilots to give sufficient priority to ensuring adequate positional awareness and given the familiarity of both pilots with the aerodrome noted that complacency had probably been a contributor factor.)
- SB20, vicinity Billund Denmark, 2015 (On 10 December 2015, a Saab 2000 descended below the prescribed vertical profile in IMC during a LLZ-only approach to Billund. An EGPWS ‘PULL UP’ warning was followed by a go around instead of the prescribed response to such a warning. A minor level bust and configuration exceedance followed after which the aircraft returned to its departure airport. Prior to the LLZ-only approach, an attempt to continue with an ILS approach to the same runway with only a LLZ signal available had also ended in a go around. In both cases, there was a complete failure to maintain vertical situational awareness.)
- H25B, vicinity Akron OH USA, 2015 (On 10 November 2015, the crew of an HS 125 lost control of their aircraft during an unstabilised non-precision approach to Akron when descent was continued below Minimum Descent Altitude without the prescribed visual reference. The airspeed decayed significantly below minimum safe so that a low level aerodynamic stall resulted from which recovery was not achieved. All nine occupants died when it hit an apartment block but nobody on the ground was injured. The Investigation faulted crew flight management and its context - a dysfunctional Operator and inadequate FAA oversight of both its pilot training programme and flight operations.)
- B733, vicinity Kosrae Micronesia, 2015 (On 12 June 2015, a Boeing 737-300 crew forgot to set QNH before commencing a night non-precision approach to Kosrae which was then flown using an over-reading altimeter. EGPWS Alerts occurred due to this mis-setting but were initially assessed as false. The third of these occurred when the eventual go-around was initially misflown and descent to within 200 feet of the sea occurred before climbing. The Investigation noted failure to action the approach checklist, the absence of ATC support and the step-down profile promulgated for the NDB/DME procedure flown as well as the potential effect of fatigue on the Captain.)
- FA20, vicinity Kish Island Iran, 2014 (On 3 March 2014, a Dassault Falcon 20 engaged in navigation aid calibration for the Regulator was flown into the sea near Kish Island in dark night conditions. The Investigation concluded that the available evidence indicated that the aircraft had been inadvertently flown into the sea as the consequence of the crew experiencing somatogravic illusion. It was also noted that the absence of a functioning radio altimeter and pilot fatigue attributable to the long duty period was likely to have exacerbated the pilots' vulnerability to this illusion.)
- A306, vicinity Birmingham AL USA, 2013 (On 14 August 2013, a UPS Airbus A300-600 crashed short of the runway at Birmingham Alabama on a night IMC non-precision approach after the crew failed to go around at 1000ft aal when unstabilised and then continued descent below MDA until terrain impact. The Investigation attributed the accident to the individually poor performance of both pilots, to performance deficiencies previously-exhibited in recurrent training by the Captain and to the First Officer's failure to call in fatigued and unfit to fly after mis-managing her off duty time. A Video was produced by NTSB to further highlight human factors aspects.)
- B772, San Francisco CA USA, 2013 (On 6 July 2013, an Asiana Boeing 777-200 descended below the visual glidepath on short finals at San Francisco after the pilots failed to notice that their actions had reduced thrust to idle. Upon late recognition that the aircraft was too low and slow, they were unable to recover before the aircraft hit the sea wall and the tail detached. Control was lost and the fuselage eventually hit the ground. A few occupants were ejected at impact but most managed to evacuate subsequently and before fire took hold. The Probable Cause of the accident was determined to be the mismanagement of the aircraft by the pilots.)
- Fatigue and Sleep Management Brochure;
- Personal Strategies for Decreasing the Effects of Fatigue in Air Traffic Control;
- Rostering: Fatigue Constraints and Guidelines
- Aircrew Fatigue: A Review of Research Undertaken on Behalf of the UK Civil Aviation Authority.
- EASA Flight Time Limitations (FTL) - Q&A, Aug 2015.
- Advisory Circular 120-100: Basics of Aviation Fatigue, June 2010
- FAA Advisory Circular 117-3: Fitness for Duty, October 2012
- IATA Fatigue Risk Management Guide for Airline Operators, 2nd edition, 2015
- Fighting Pilot Fatigue, video by Boeing’s Fatigue Risk Management team in partnership with Delta airlines to portray the effects of fatigue on pilots. It describes technologies in the flight deck that can monitor and prevent fatigue-related events.
- Operator's Manual: Human Factors in Aviation Maintenance, FAA, 2014.
- Safety Behaviours: Human Factors Resource Guide for Engineers, CASA (Australia), 2013. Chapter 5 describes the causes and impacts of fatigue, and strategies to manage it (for maintenance personnel).
- Human Performance and Fatigue Research for Controllers, Gawron et al., 2011.
- FAA Fact Sheet – Sleep Apnea in Aviation, Feb 2015.
- Coping with long range flying. Recommendations for crew rest and alertness., Airbus, Cabon, P., et al., Nov 1995.
- Fatigue and Alertness Management in Aviation
- Being Prepared for the Outbound Flight - Checklist
- Being Prepared for the Return Flight in Eastward Rotations - Checklist
- Being Prepared for the Return Flight in North and South Rotations - Checklist
- Being Prepared for the Return Flight in Westward Rotations - Checklist
- CASA Fatigue Risk Management System Handbook, 2013
- CANSO Fatigue Management Expert Group